PC-cell-derived growth factor (“PCDGF”) is an 88-kDa glycoprotein autocrine growth factor expressed in a tightly regulated fashion in normal cells but overexpressed and unregulated in tumorigenic cells. Inhibition of PCDGF expression or activity inhibits the growth of tumorigenic cells. PCDGF is composed of a 68-KDa protein core and a 20-KDa carbohydrate moiety. PCDGF belongs to a novel family of double cysteine rich polypeptides and was originally isolated from the culture medium of the highly tumorigenic mouse teratoma-derived cell line PC. PCDGF has been shown to be overexpressed in mouse and human tumors including liver, kidney, breast, bone, bone marrow, testes, brain, ovary, skin, and lung.
Amino-acid and cDNA sequencing indicated that PCDGF is identical to the precursor of epithelins/granulins first purified as 6 KDa double cysteine-rich polypeptides from rat kidney or human granulocyte extracts. The granulin/epithelin precursor was previously thought to be inactive. See U.S. Pat. No. 5,416,192. However, Serrero et al. demonstrated that PCDGF is a highly active, tumorigenic protein associated with a variety of tumor cell types. See U.S. Pat. No. 6,309,826. The degree of overexpression of PCDGF positively correlates with the degree of tumorigenicity of cells. Id.
PCDGF is a growth modulator for a variety of cell lines, including fibroblasts, PC cells, and mammary epithelial cells. Comparison of the expression of PCDGF in the highly tumorigenic PC cells and in parent 1246 cells demonstrated that PCDGF expression was very low in the non-tumorigenic cells and was overexpressed in the highly tumorigenic cells. The same result was observed in human breast carcinomas where PCDGF expression was very low in non-tumorigenic mammary epithelial cells and increased in breast carcinoma cells.
PCDGF antagonists (e.g., anti-PCDGF antibodies and PCDGF antisense nucleic acids) inhibit or interfere with the activity of PCDGF and with the growth of tumorigenic cells. Zhang, H., and G. Serrero, 1998, PNAS 95, no. 24:14202; Lu, R., and G. Serrero, 2000, PNAS 97, no. 8:3993. In both teratoma-derived cells and breast cancer cells, PCDGF activity was inhibited by treating the cells with an anti-PCDGF neutralizing antibody or by transfecting the cells with an antisense PCDGF cDNA. Treatment of cells with PCDGF antagonists in teratoma cells or breast carcinoma cells completely inhibited cell proliferation and tumorigenesis in vivo. Id.
Antibodies are specialized proteins capable of binding a target molecule with great specificity. Originally identified as naturally produced protein products of the animal immune system, antibodies function as a primary arm of the immune system by binding to and facilitating clearance of micro-organisms and other foreign substances from the body. Antibodies, also known as immunoglobulins (Ig), are generally formed from two “light” chains and two “heavy” chains. The carboxy terminus of the chains forms the constant or Fc region of the antibody while the amino terminus forms the variable or antigen-binding domain. There are at least five isotype categories of antibodies: IgG, IgE, IgA, IgM, and IgD. Each Ig isotype interacts with different effector cells resulting in different biological activities. For example, IgG marks foreign antigens for clearance by white blood cells (e.g., T cells) while IgE, located on the surface of mast cells, triggers allergic responses to particular antigens.
Animal models for generating antibodies are useful for making large quantities of antibodies directed to a desired antigen. However, human immune responses against “foreign” antibodies limit the therapeutic usefulness of antibodies developed in animals. “Humanized” antibodies substitute the complementarity determining regions (“CDRs”) of animal antibodies with human CDRs resulting in a greatly reduced immune response in humans to the “foreign” antibody. See, e.g., Winter (British Application Number GB2188538A).
An anti-idiotypic antibody (“anti-IdAb”) is an antibody that recognizes unique determinants generally associated with the antigen-binding site of an antibody. An anti-IdAb can be prepared by immunizing an animal of the same species and genetic type (e.g., mouse strain) as the source of the mAb with the mAb to which an anti-IdAb is being prepared. The immunized animal will recognize and respond to the idiotypic determinants of the immunizing antibody by producing antibody to these idiotypic determinants (the anti-IdAb). The anti-IdAb may also be used as an immunogen to produce an immune response in yet another animal, producing a so-called anti-anti-IdAb. The anti-anti-IdAb may be epitopically identical to the original mAb which induced the anti-IdAb. Thus, antibodies directed to the idiotypic determinants of an mAb can be used to generate antibodies of identical specificity to the original InAb.
U.S. Pat. No. 6,309,826 refers to the existence of PCDGF receptors on cell surfaces of several cell lines, including the mammary epithelial cell line C57MG, the 1246 and PC cell lines, and the mink lung epithelial cell line CCL64. In these studies, the PCDGF receptor was detected by binding labeled PCDGF to the PCDGF receptor and detecting the presence of PCDGF bound to its receptor on the cell surface. What is needed are PCDGF receptor antibodies and methods for binding to cell surfaces to interfere with the activity of the PCDGF receptor and the tumor promoting activity of PCDGF.